In situ PXRD analysis on the kinetic effect of PVP-K90 and PVCap on methane hydrate dissociation below ice point

natural gas transportations due to economic and environmental factors. To understand the kinetic performance of KHIs comprehensively, dissociations of CH4 hydrates in the presence of PVP-K90 and PVCap were investigated below ice point. Cryo-SEM and in situ PXRD were used to provide a microscopic insight on the dissociation kinetics. Results showed that a typical CH4 hydrate dissociation at 268 K could be divided into 4 stages. The selfpreservation effect took place in the second stage accompanied with an rise in the ratio of Ih(002) to Ih(100) peaks from 0.5 to 1.1. About 30% of CH4 hydrates were suggested to dissociate into plate-like ice to form ice coatings on hydrate surface. In the presence of PVP-K90 or PVCap, the self-preservation stage reduced greatly and the initial dissociation rates of CH4 hydrates were found enhanced as the concentrations of the KHIs.increased from 0.5 to 2.0 wt%. SEM images revealed that PVP-K90 was suggested to be included in the small ice crystals embedded in hydrate phase and hinder the connections of the plate-like ice crystals on hydrate surface, while PVCap was found to induce a dendritic growth of CH4 hydrate, leading to a surge in the specific surface area of CH4 hydrates which was not beneficial to the formation of ice coatings on hydrate phase. Therefore, both PVP-K90 and PVCap promoted hydrate dissociation below ice point by inhibiting the formation of selfpreservation effect.

由于经济和环境因素的天然气运输。为了全面了解动力学抑制剂（KHIs）的动力学性能，在冰点以下研究了在聚乙烯吡咯烷酮 - K90（PVP - K90）和聚乙烯基己内酰胺（PVCap）存在下甲烷水合物的分解。低温扫描电子显微镜（Cryo - SEM）和原位粉末X射线衍射（in situ PXRD）被用于对分解动力学提供微观见解。结果表明，在268 K时典型的甲烷水合物分解可分为4个阶段。自保护效应在第二阶段发生，同时 Ih(002)与Ih(100)峰的比值从0.5上升到1.1。约30%的甲烷水合物被认为分解成片状冰，在水合物表面形成冰层。在PVP - K90或PVCap存在的情况下，自保护阶段大幅减少，并且随着动力学抑制剂浓度从0.5%增加到2.0%（重量比），发现甲烷水合物的初始分解速率提高。扫描电子显微镜图像显示，PVP - K90被认为包含在嵌入水合物相的小冰晶中，并阻碍水合物表面片状冰晶的连接，而发现PVCap诱导甲烷水合物的树枝状生长，导致甲烷水合物的比表面积激增，这不利于在水合物相上形成冰层。因此，PVP - K90和PVCap都通过抑制自保护效应的形成促进了冰点以下的水合物分解。